1. Field of the Invention
The present invention relates to method of controlling movable members driven by an electric motor.
2. Background Art
Different systems and methods for controlling a mobile member driven by a multi-pole permanent magnet direct current electric motor are known, making use of the undulations produced in the consumption current thereof as it circulates through each one of the inductors forming it.
Patent application GB-A-2060944 proposes a device to control the position of a seat moved by a multi-pole motor. By means of the monitoring of the current circulating through the different poles of the motor, the counting of pulses generated by each one of the poles is carried out and is compared with a reference, which enables determining the seat position. A memory is proposed which has stored therein a series of desired positions which can be selected to force the seat to move until it reaches the selected position. Said memory, as well as the logic used by the device, are integrated in a microprocessor.
A similar but somewhat more advanced proposal is that carried out by patent application EP-A-0997341, which relates to a control device for a movable member including a direct current motor, said device operating such that it memorizes a specific position of the movable member, and although the member is moved to another position, it can be returned to the memorized position by means of a simple switching operation. A pulse generating circuit according to the ripple of said motor, for finding out the position of the movable member at all times and to thus compare it with the memorized position so as to actuate the motor in one direction or the other until reaching said memorized position, is also proposed. The proposed control allows adjusting the movable member, such as a seatback, for example, to different user profiles. To offset the movements of the motor due to inertia, the memorization of a series of correction values which have been experimentally obtained for different motors is proposed.
Although said second background document, unlike the first one, takes into account the movements of the motor not produced by the application of voltage, but rather by inertia, it does not contemplate any other type of causes which can distort the measurements obtained when monitoring the intensity, such as interferences. Nor does it develop a method for achieving said position correction, but rather it simply explains that the memorized correction values have been obtained experimentally.
None of said background documents takes into account either the different behavior of the motor depending on whether said motor is operating in a transient state, such as the start-up, or in a steady state.